There is a need to be able to identify various hydrocarbon fuels, such as gasolines, kerosines, jet fuels, diesel fuels heating oils and heavy fuel oils, from the points of view both of type and origin. Identification of the origin of spillages, and detection of counterfeiting or fraud are examples of such need.
U.S. Pat. No. 5,234,475 (ass. SRI International) indicates that prior art attempts to use dyes, detection of which would be by fluorescence, have suffered from the problem that gasoline and other fuel fluorescence strongly in the absence of added dye. Furthermore, in the case of spills, dyes tend to adsorb onto soil and become eliminated from spilled fuel.
In order to seek to overcome such problems, U.S. Pat. No. 5,234,475 provides for incorporation into hydrocarbon fuels of quantities of one or more fullerene derivatives. Such materials are described as clustered carbon structures generally spherical in shape and having a carbon content generally ranging from about 50 to about 90 carbon atoms, those having the structures C.sub.60 (buckminsterfullerene), C.sub.70, C.sub.74, C.sub.76, C.sub.78, C.sub.82, C.sub.84, C.sub.86, C.sub.88, C.sub.90, C.sub.92 and C.sub.94 being specifically mentioned (Col. 2, lines 25 to 30). Identification may be by mass spectroscopy, UV-visible spectroscopy or high pressure liquid chromatography (HPLC) (Col. 2, lines 50 to 60).
U.S. Pat. No. 5,474,937 (ass. Isotag) describes a method for identifying the source of a transported chemical shipment, such as crude oil. This method employs a chemical element or an organic compound with one or more atoms which are non-radioactive isotopes generally not found in nature. Identification of samples as marked material is by comparison with an authentic sample of marked material. Preferred compounds are deuterated compounds or those rendered isotopic by carbon-13, fluorine- 19, nitrogen- 15, oxygen- 17 and oxygen- 18. Gas chromatography and mass spectroscopy are mentioned as appropriate analysis techniques. The examples relate to crude oil. Example 1 uses deuterated octane. Example 2 uses deuterated acetone. Example 3 does not use any specified isotopes, but employs a mixture of tetrafluoroethylene, chloroform and trichloroethylene in "the ratio" 1:3:7.
Each of these prior art approaches has the disadvantage either that it employs unusual or not readily obtainable additive or additives or that it employs one or more additives which are chemically different from anything else which might be present in the liquid to be identified, and which therefore may have the potential to interact adversely with one or more performance additives which might be incorporated when the liquid to be identified is a hydrocarbon fuel.